Q. No.In a water body polluted with biodegradable organic compounds,
1. the BOD and DO content are low
2. the BOD and DO content are high
3. the BOD is low and DO content is high
4. the BOD is high and DO content is low
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The following diagram shows the effect of sewage discharge on some important characteristics of a river. What can be A and B respectively?
| 1. | BOD and DO | 2. | DO and BOD |
| 3. | BOD and COD | 4. | COD and BOD |
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Consider the following statements:
| I: | Freshwater algal blooms, the result of an excess of nutrients [particularly phosphates] cause large scale fish mortality. |
| II: | Algae grow very quickly under high nutrient availability, but each alga is short-lived, and the result is a high concentration of dead organic matter, the decay of which consumes dissolved oxygen in the water, resulting in hypoxic conditions. |
1. Both I and II are correct and II explains I
2. Both I and II are correct but II does not explain I
3. I is correct and II is incorrect
4. Both I and II are correct
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In an algal bloom, the cause of death of other algae is usually:
1. toxins
2. decreased DO
3. decreased sunlight
4. decreased nutrients
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Algal blooms impart a distinct colour to water due to:
| 1. | Their pigments |
| 2. | Excretion of coloured substances |
| 3. | Formation of coloured chemicals in water facilitated by physiological degradation of algae |
| 4. | Absorption of light by algal cell wall |
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The world’s most problematic aquatic weed, “The terror of Bengal”, is the name given to:
| 1. | Zostera | 2. | Ceratophyllum |
| 3. | Eichhornia | 4. | Parthenium |
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| I: | At least 1.0% impurities must be present in a sample of domestic sewage to make it unfit for human use. |
| II: | Waste water from industries often contains toxic heavy metals like mercury, cadmium, copper and lead that have a density greater than 5 gm/cm3. |
2. Both Statement I and Statement II are correct
3. Only Statement II is correct
4. Only Statement I is correct
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Apart from DDT, what else is known to undergo biological magnification in aquatic food chain?
| 1. | Nitrates | 2. | Phosphates |
| 3. | Mercury | 4. | Calcium |
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| 1. | A to B |  |
| 2. | B to C | |
| 3. | C to D | |
| 4. | D to E |
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| Assertion (A): | Predatory fish such as swordfish and sharks or birds like osprey and eagles have higher concentrations of mercury in their tissue than what could be accounted for by direct exposure alone. |
| Reason (R): | Mercury [or methyl mercury] undergoes biomagnifications in aquatic food chains. |
| 1. | Both (A) and (R) are true and (R) is the correct explanation of (A). |
| 2. | Both (A) and (R) are true but (R) is not the correct explanation of (A). |
| 3. | (A) is true but (R) is false. |
| 4. | Both (A) and (R) are false. |
- If both the assertion and the reason are true and the reason is a correct explanation of the assertion
- If both the assertion and reason are true but the reason is not a correct explanation of the assertion
- If the assertion is true but the reason is false
- If both the assertion and reason are false
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